A retransmitting process (ARQ (automatic repeat request)) for a loss of a packet in an IP (Internet protocol) network is to determine a loss of a packet depending on a reply of an ACK (normal reply) or a NACK (abnormal reply), and retransmit a lost packet.
When the ARQ is applied to a multicast communication or an ALM (application layer multicast), the following problem occurs.
That is, after a lost packet is corrected and prepared data is transferred to a downstream terminal, there occurs a correction delay. As illustrated in FIG. 18, an upstream correction delay propagates to downstream, a delay is added each time a loss occurs, and a buffer overflows in a downstream terminal.
Related Art 1: To suppress the above-mentioned correction delay, a packet is transferred even in a correcting (retransmitting) process in the related art. FIG. 19 is the outline of the retransmitting process according to the related art. In this method, since loss information about a packet is propagated to a downstream terminal, a retransmission request from each terminal to which the information is propagated is suppressed. Furthermore, a correction is made in a downstream terminal by multicasting a retransmission packet.
Related Art 2: Networks and communication devices have a parent-child relation and a brother-relation in an ALM, and an ACK or a NACK is transmitted to an elder brother (parent if there is no elder brother). Thus, there occurs no congestion of replies of ACKs or NACKs, or retransmissions of packets, and the increase of traffic is distributed, thereby suppressing the overflow of a buffer in a terminal functioning as a leaf.
Patent Document 1: Japanese Laid-open Patent Publication No. 2007-228064
Patent Document 2: Japanese Laid-open Patent Publication No. 2004-318274
Patent Document 3: Japanese Laid-open Patent Publication No. 2004-199578